Cars can brake for pedestrians if drivers don't

The developers of the first pedestrian collision mitigation system available in the United States drove about half a million miles in cities around the globe to gather the necessary information about pedestrians — and about things a computer might mistake for them.

"The most difficult part is actually to make sure that the car does not brake when it's not supposed to," says Thomas Broberg, senior technical adviser for safety at Volvo. "You would never accept a car that brakes every time you pass a mailbox."

Introduced last year on the S60 sedan, Volvo's system, dubbed Pedestrian Detection, is now an option on several Volvo models sold in the United States. The system uses radar combined with a camera to identify potential collisions with both pedestrians and the rear-ends of other vehicles and motorcycles. It first warns a driver of an impending crash and then brakes automatically if the driver doesn't respond.

Subaru has developed a similar system, but so far it's only available in Japan. Other automakers are close behind. Audi, for example, is working on a system that, unlike Volvo's, promises to work in the dark. That's important because most fatal pedestrian crashes take place at night.

Automatic braking

In Volvo's system, if the driver isn't taking action, a warning sounds and a red light meant to resemble another vehicle's brake lights appears in the windshield. If the driver still doesn't respond, the car stops itself. The Swedish automaker says the system can avoid a crash completely at speeds up to 22 mph. Beyond that, it's about reducing the speed of the impact and, therefore, the consequences of the crash. The feature can function at speeds as fast as 50 mph.

Volvo estimates the feature could reduce by 24 percent pedestrian deaths caused by frontal crashes if it were adopted universally.

In addition to being dependent on light, the Volvo system has a few other limitations. It won't spot a person shorter than 31.5 inches or in a wheelchair, nor is it programmed to react to cyclists or animals. If a driver's view of a pedestrian is blocked, the camera won't be able to see the person either. However, it should work in what the Institute has identified as the most common scenario — a driver going straight with a clear view and a pedestrian crossing traffic.

Volvo suffered a few well-publicized failures during demonstrations for journalists. Video footage shows an S60 crashing into a dummy instead of stopping. Broberg says in the vast majority of demonstrations the system has worked as advertised, and the mishaps that did occur were a result of the technology's sophistication. The system, he says, is "hard to trick" because it's programmed to recognize only a flesh-and-blood person.

Pedestrian Detection is distinct from Volvo's City Safety, which uses a less expensive laser sensor and is aimed at avoiding rear-end crashes with other vehicles at low speeds only. Pedestrian Detection is an optional feature, raising the question of whether people are prepared to pay more to protect others. But the system also appeals to people's self-interest because it prevents rear-end crashes with other vehicles and because it's part of a bigger technology package that includes things like adaptive cruise control. The company estimates it will have a take rate of 20-25 percent globally.

Volvo’s Pedestrian Detection uses radar and a camera to identify people who might end up in the car’s path. If the system determines a collision is imminent, it first alerts the driver with an audible warning and a red light in the windshield (above). If the driver doesn’t respond, the vehicle brakes itself. The system also reacts to the rear-ends of other vehicles and motorcycles.

Broberg says Volvo decided to do something about pedestrians because they account for such a large share of fatalities — 12 percent in the United States and an even larger share in Europe. Volvo and other automakers, spurred on by European regulators, have modified the fronts of vehicles to make them "softer" if they contact a pedestrian. It's not clear yet how much such changes will help. Broberg, for his part, is skeptical.

"Unfortunately, the laws of physics are against us there. … Two tons of steel versus 80 kilograms of flesh," he says. "So our belief has been that we need to try to help the drivers avoid these types of collisions."

What other manufacturers are doing

Subaru's EyeSight system, which is available in Japan, is similar to Volvo's, but the latest version relies on two cameras to produce stereo vision, instead of radar and a single camera. The company says that helps keep down the cost.

Subaru says its system can recognize both pedestrians and cyclists. As with Volvo's technology, EyeSight also is activated if the car gets too close to the vehicle in front of it and can brake automatically if the driver doesn't respond to warnings.

Audi, meanwhile, is working on a pedestrian avoidance system that it says will work in all light conditions. It uses a relatively new technology known as a PMD sensor, or photonic mixer device, to detect obstacles in the road. The system is designed to automatically brake if a crash with a pedestrian or large animal is unavoidable. It also avoids some collisions with other vehicles. The system is expected to reach consumers within the next three years.

Audi already has a separate system that alerts drivers to the presence of pedestrians at night. The night vision assistant uses a thermal imaging camera to highlight people on a dashboard display.

Both Mercedes and BMW have similar night vision features. BMW is developing a camera-based pedestrian detection system with automatic braking, and Mercedes is enhancing existing crash avoidance systems to react to pedestrians as well as other vehicles.